1. Field of the Invention
The present invention relates to a continuous process for manufacturing a porous material, and in particular, to a continuous process for manufacturing a porous material using template techniques in a roll-to-roll manner.
2. Description of the Related Art
Generally, porous materials are materials with porous structures. According to International Union of Pure and Applied Chemistry (IUPAC), porous materials can be divided into three types, such as microporous, mesoporous, and macroporous materials. The microporous materials comprise pores of diameters substantially less than 2 nm, the macroporous materials comprise pores of diameters substantially greater than 50 nm, and the mesoporous materials comprise pores of diameters among 2-50 nm.
Surfactants typically comprise organic amphiphilic molecules having hydrophilic and hydrophobic groups and can be dissolved in organic solutions and aqueous solutions. When surfactant concentration in water is low, molecules of the surfactants will be located at the interface between air and water. When surfactant concentration in water is increased to a level causing saturated absorption at an interface between air and water, the surfactants not absorbed at the interface will aggregate with each other to make the hydrophilic ends face outward and contact with water molecules to reduce a contact area between the water molecules and the hydrophobic groups. The surfactant aggregates are so-called “micelle,” and a surfactant concentration when the micelle is formed is defined as a critical micelle concentration (CMC).
A hydrophilic-lipophilic balance (HLB) of a surfactant is the hydrophilic degree of the surfactant. A surfactant with higher HLB value has higher hydrophilicity. For example, surfactants with HLB values of 8 or higher have high water solubility.
Since the solution concentration is greater than the critical micelle concentration, surfactant molecules will aggregate to form the micelle. Although the micelle is typically formed in a spherical shape, the size and shape of the micelle can be gradually changed in accordance with variations in concentration and temperature. In addition, the size and shape of the micelle are also influenced by the chemical structure and molecular weight of the surfactant. Based on formation conditions and compositions, liquid crystals comprise thermotropic liquid crystals and lyotropic liquid crystals. The thermotropic liquid crystals are formed due to temperature variations and the lyotropic liquid crystals are formed due to concentration variations.
Based on the organization of molecules or surfactant aggregates, liquid crystals comprise smectic and nematic mesophase. In the nematic phase, all molecules or surfactant aggregates are aligned approximately parallel to each other, with only a one-dimensional (orientational) order. In smectic phase, all molecules or surfactant aggregates exhibit both (two-dimensional) positional and orientational order.
In the prior art, one of the manufacturing processes for ordered mesoporous materials uses various surfactants as structure-directing agents, or so-called templates. The surfactants can be, for examples, triblock copolymers, diblock copolymers or ionic surfactants. The above method also uses alkoxides as precursor to synthesize metal oxides or hydroxides by a sol-gel technique. Alternatively, the above method may use carbonaceous monomers or oligomers as precursors of carbons to mix with surfactants and then the surfactants are removed as the surfactants are orderly arranged and the precursors are polymerized. The obtained polymers are then carbonized at a high temperature such that highly ordered mesoporous carbons are obtained. However, the research to date about formation of the mesoporous materials mainly focuses on changing the synthesis conditions of the precursors or the materials. For example, U.S. Pat. Nos. 5,057,296; 5,108,725; 5,102,643; and 5,098,684 disclose using ionic surfactants as a template for manufacturing porous materials, wherein pore sizes thereof are greater than 5 nm. However, the formed mesoporous structures are not stable.
The conventional manufacturing processes for highly ordered mesoporous materials are typically template-directed synthesis. The methods thereof can be divided into hard template methods and soft template methods according to features and restrictions of the template used therein. Since Kresge et al. disclosed a synthesis method for forming mesoporous silica in 1992 (C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, and J. S. Beck, “Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism” Nature, vol 359, no. 6397, pp. 710-712, 1992), research about manufacturing mesoporous materials by template methods have been developed in the last decade. More precisely, research about manufacturing mesoporous materials by template methods that mainly focus on selections of surfactants and the conditions of material synthesizing has been carried out. For the soft template method, through selecting the surfactants and adjusting the synthesis conditions, the surfactant as a structure-directing agent will self-assemble into a highly ordered liquid crystalline phase while the concentration of the surfactant is greater than the critical micelle concentration; thereby forming various types of highly ordered mesoporous channels such as MCM-41, SBA-15 and MCM-50 having a two dimensional high symmetry, and KIT-5, SBA-16, SBA-11, SBA-2, MCM-48, etc. having a three dimensional high symmetry. For the hard template method, a previously prepared mesoporous silicon dioxide, such as SBA-15 is used as a template to prepare reversed mesoporous materials. After mixing carbon precursors with SBA-15, the carbon precursors are converted to carbon. The silicon dioxide in the obtained product is removed by using hydrofluoric acid or strong bases and then the ordered mesoporous carbon named as CMK-3 is obtained. Although highly ordered mesoporous materials having microstructures can also be obtained, the cost of the hard template method is high, and the structures of the obtained materials are reversed mesoporous structure.
The highly ordered mesoporous materials synthesized by using surfactants as structure-directing agents have characteristics such as high specific surface areas, uniform and adjustable pore sizes, and regular pore channel arrangements such that high value in applications such as separation, catalyst, electromagnetic materials, and chemical sensing can be seen, wherein the representative materials are mesoporous silicon dioxides.
The evaporation induced self-assembly (EISA) method is a process to obtain a highly ordered arrangement of the surfactants. Due to the slow evaporation of solvents, the surfactants can be thus formed with highly ordered liquid crystalline mesophases. An amount of the prepared materials in each batch must be limited in order to obtain ordered structure. Because of the multistep and nonequilibrium of evaporating and self-assembly, the synthesis space is limited in a batch process. The solvent evaporating path through the solution-air interface and the gradient of solution concentration need to be well controlled to obtain an ordered structure. Therefore, the EISA process is preferred to be conducted in dishes rather than beakers. Due to the above mentioned limitations, the batch process cannot satisfy the need of mass production.
Chinese Patent No. 101244818A discloses using a polyurethane sponge as a skeleton, wherein a mixture comprising precursors and surfactants is coated over the skeleton for solvent evaporation induced self-assembly. Thereafter, the polyurethane sponge is thermally treated to achieve mass production of mesoporous carbon by batch process. This process still can not meet the requirement of automated mass production. Until now, it is still an unsolved problem to perform mass production with EISA process via continuous or automated routes.
Accordingly, with a scale-up design in a conventional batch process, there are disadvantages of reaction uniformity and unstable quality.